Basic and ultrabasic rocks from the Ankara Melange, Turkey

Abstract

Summary The Ankara Melange consists from west to east of three major parallel belts: (i) metamorphic melange, (ii) limestone melange and (iii) ophiolitic melange. A Triassic age for the metamoprhic and limestone belts and a Cretaceous age for the ophiolitic belt have been suggested by several authors (Norman 1973, Çapan 1981, Yilmazer 1981). The ophiolitic belt includes lenses of serpentinite, occasionally unserpentinized peridotite, gabbro, pillow lava, agglomerate and basic dykes. The ultrabasic rocks show tectonic fabrics and the gabbros cumulate textures. The metamorphic and limestone melange belts contain basic volcanic rocks only as blocks, clasts and dykes, and are devoid of ultrabasic rocks. Petrochemical studies reveal that the volcanic rocks of the ophiolitic and metamorphic belts are very similar in mineralogical and chemical composition, including representatives of both the tholeiitic and calc-alkaline series. The presence of almost all the members of an ophiolite suite may indicate an ocean floor origin for the ultrabasic and basic rocks of the ophiolitic melange belt, and the occurrence of calc-alkaline rocks in both belts may suggest at least one phase of island arc volcanism. These rocks may represent several phases of rifting and island arc generation during the evolution of the Mediterranean Tethyan domain.